1. Technical Field of Invention
The present invention relates, generally, to power regulation systems and, in particular, to providing precisely regulated power to a microelectronic device such as a microprocessor. Improved power regulation is accomplished with a fine resolution pulse width generator.
2. Background of the Invention
Regulated power supplies or voltage regulators are typically required to provide the voltage and current supply to microelectronic devices. The regulator is designed to deliver power from a primary source to an electrical load at the specified current, voltage, and power efficiency. Switching power converters (SPC) also referred to as Buck regulators are commonly used voltage regulators due to their high efficiency, high current capability, and topology flexibility. In addition, they can be designed to provide very precise voltage and current characteristics required by devices such as microprocessors, microcontrollers, memory devices, and the like.
Power requirements for emerging leading edge technology microprocessors have become very difficult to satisfy. As the speed and integration of microprocessors increases, the demands on the power regulation system increase. In particular, as gate counts increase, the power regulation current demand increases, the operating voltage decreases and transient events (e.g. relatively large voltage spikes or droops at the load) typically increase in both magnitude and frequency. Some emerging microprocessors are expected to run on less than 1.3 volts and more than 100 amperes.
SPC's utilizing step-down multi-phase Buck converters have been the preferred topology to meet the low voltage and high current requirements of microprocessors. With the advent of increasingly complex power regulation topologies, digital techniques for power converter control, specifically in multiphase designs, can improve precision and reduce the system's total parts count while also supporting multiple applications in the same power system through digitally programmable feedback control.
However, one of the difficulties in implementing digital multiphase buck converters is in the generation of precise width pulses to control the power switch. Since the width of the pulse has a direct impact on the voltage at the load, it is a key performance limiter if the system is unable to generate a pulse width with the desired precision.
Analog controllers typically use a precise sawtooth generator and a comparator to determine how wide a pulse to generate. The compensator or loop filter in the controller senses the voltage at the load and generates a voltage corresponding to the desired pulse width. The beginning of the output pulse is lined up to the beginning of the sawtooth waveform each period. The comparator compares the sawtooth generator with the compensator output to determine when the end of the output pulse should occur.
In a digital controller, the voltage (or current) sensed at the load is digitized using an analog to digital converter. Such a previously disclosed digital multiphase buck converter will be described in greater detail in connection with FIG. 1. Briefly, a target voltage is computed based on either a preset requirement or the user inputs, such as the voltage identification (VID) control word. The difference between the sensed voltage and target voltage is the error voltage, which is applied to a digital compensator or loop filter. The compensator transfer function is computed in such a way as to provide stable closed loop operation of the regulator, while maximizing the performance such as bandwidth of the loop. The compensator adjusts the width of the output pulse, increasing or decreasing the load voltage to drive the error voltage to zero, thus regulating the voltage at the load.
The digital compensator output is a representation of the desired pulse width. This output is scaled (i.e. multiplied) by a multiplier constant to generate a value that is used by the pulse width modulation generator (PWM) to generate a pulse of the desired width for that cycle. The pulse width modulation generator (PWM) typically uses a counter to generate a desired pulse width. The counter runs off a higher frequency clock such that the output pulse widths are integral multiples of the high frequency period (or half period if both edges of the clock are used by the counter). Since the width of the pulse generated in this manner is discrete, there is a quantization error associated with each pulse width.
Digital controllers attempt to reduce this quantization error through various techniques. One such technique, for example, is to simply run the counter clock at a higher frequency so that the discrete steps required are smaller. This technique however is limited when the technology will not support a higher clock frequency. In addition, a higher frequency counter would require an increase in power dissipation in order to support the higher clock frequency. By way of further example, another technique is to use a finer resolution delay generator, such as a chain of inverters. This technique is primarily limited by the inability to control the delay in this fine resolution delay generator, so that the controller is not able to generate the desired pulse width with high precision.
Accordingly, improved techniques for precisely controlling the width of pulses generated by pulse width modulators (PWM) in digital multiphase controllers are needed. In particular, techniques that improve the accuracy and reduce the effects of quantization in digital pulse generators are desired.